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From: "avi at scylladb dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/105373] miscompile involving lambda coroutines and an
 object bitwise copied instead of via the copy constructor
Date: Thu, 28 Apr 2022 17:28:19 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105373

--- Comment #11 from Avi Kivity <avi at scylladb dot com> ---
Created attachment 52899
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D52899&action=3Dedit
simple(r) reproducer

I was able to reduce it to something simple (102 lines), but I was only abl=
e to
verify that wrong code is generated on the gimple level (where my understan=
ding
is very limited). Still, to my inexperienced eyes it looks like an object w=
ith
a copy constructor is being copied bitwise.

Compile with (gcc 11.3.1)

    g++ -Wfatal-errors -w -std=3Dgnu++20  -march=3Dwestmere -fvisibility=3D=
hidden  -c
-o table.o table.i -fdump-tree-gimple -g=20

and observe in table.i.006t.gimple:

    struct lw_shared_ptr D.2740 [value-expr: frame_ptr->D.2740_4_5];

and then

    frame_ptr->D.2741_4_5.__old4 =3D frame_ptr->D.2740_4_5;


in other places, variables of the same type are copied using the copy
constructor.=